1. Field of the Invention
The present invention relates to a process for producing a hydrogen absorbing alloy powder, and particularly to a process for producing a hydrogen absorbing alloy powder which is an aggregate of alloy particles each comprising a metal matrix and added-components, by conducting one of mechanical alloying and mechanical grinding, using an aggregate of metal matrix particles and an aggregate of added-component particles. The present invention also relates to a hydrogen absorbing alloy powder and to a hydrogen-storing tank including such hydrogen absorbing alloy powder therein.
2. Description of the Related Art
In this type of the producing process, a method is conventionally employed, in which metal matrix particles and added-component particles having the same particle size (usually 1 xcexcm or more) or the substantially same particle size are used, and relatively hard added-component particles are sufficiently finely-milled, and then made to penetrate and dispersed uniformly into the metal matrix particles.
However, the above conventional process suffers from a problem that milling must be carried out, for example, for several ten hours in order that the added-component particles may be finely milled and made to penetrate and dispersed uniformly, resulting in an increased manufacture cost for the hydrogen absorbing alloy powder.
Various hydrogen absorbing alloy powders are conventionally known. However, the conventionally known hydrogen absorbing alloy powders are accompanied by a problem that a hydrogen storage capacity and a rate of hydrogen absorption/desorption are insufficient for the purpose of using such hydrogen absorbing alloy powder as being mounted in a fuel cell electric vehicle.
Accordingly, it is an object of the present invention to provide a process for producing a hydrogen absorbing alloy powder of the above-described type, wherein the milling time can be shortened remarkably.
To achieve the above object, according to the present invention, there is provided a process for producing a hydrogen absorbing alloy powder which is an aggregate of alloy particles each comprising a metal matrix and added-components, by conducting one of a mechanical alloying and a mechanical grinding, using an aggregate of metal matrix particles and an aggregate of added-component particles, wherein the relationship between the particle size D of the metal matrix particles and the particle size d of the added-component particles is set at dxe2x89xa6D/6.
When the hydrogen absorbing alloy powder is produced by employing mechanical alloying or the like, metal matrix particles having a particle size D of about 5 xcexcm are usually used. Therefore, the particle size d of the added-component particles is equal to or smaller than 834 nm (dxe2x89xa6834 nm) in the case of D=5 xcexcm, because the particle size d of the added-component particles is set at dxe2x89xa6D/6. The added-component particles having such a particle size are fine particles or ultra-fine particles and have a very high activity. Therefore, not only by making the added-component particles penetrate into the metal matrix particles, but also by retaining the added-component particles on surfaces of the metal matrix particles, a highly active hydrogen absorbing alloy powder can be produced. In addition, the metal matrix particles are fine or ultra-fine particles and hence, it is unnecessary to finely mill the metal matrix particles by milling.
Thus, according to the above-described process, it is possible to remarkably shorten the milling time for producing the hydrogen absorbing alloy powder, for example, from 40 hours to 15 minutes. However, when the relationship between the particle sizes D and d is d greater than D/6, the milling time is longer, and the producing energy is inefficient.
It is another object of the present invention to provide a hydrogen absorbing alloy powder of the above-described type which is suitable to be used for mounting in a vehicle, and which presents a large hydrogen storage capacity and a high rate of hydrogen absorption/desorption.
To achieve the above object, according to the present invention, there is provided a hydrogen absorbing alloy powder which is an aggregate of alloy particles each including an Mg matrix and a plurality of ultra-fine particles dispersed in the Mg matrix, the Mg matrix including a plurality of Mg crystals having a grain size DC in a range of 1.0 xcexcmxe2x89xa6DCxe2x89xa6500 xcexcm, and the ultra-fine particles having a particle size d0 in a range of 10 nmxe2x89xa6d0xe2x89xa6500 nm, the ultra-fine particles being at least one type selected from the group consisting of Ni ultra-fine particles, Ni alloy ultra-fine particles, Fe ultra-fine particles, Fe alloy ultra-fine particles, V ultra-fine particles, V alloy ultra-fine particles, Mn ultra-fine particles, Mn alloy ultra-fine particles, Ti ultra-fine particles, Ti alloy ultra-fine particles, Cu ultra-fine particles, Cu alloy ultra-fine particles, Al ultra-fine particles, Al alloy ultra-fine particles, Pd ultra-fine particles, Pd alloy ultra-fine particles, Pt ultra-fine particles, Pt alloy ultra-fine particles, Zr ultra-fine particles, Zr alloy ultra-fine particles, Au ultra-fine particles, Au alloy ultra-fine particles, Ag ultra-fine particles, Ag alloy ultra-fine particles, Co ultra-fine particles, Co alloy ultra-fine particles, Mo ultra-fine particles, Mo alloy ultra-fine particles, Nb ultra-fine particles, Nb alloy ultra-fine particles, Cr ultra-fine particles, Cr alloy ultra-fine particles, Zn ultra-fine particles, Zn alloy ultra-fine particles, Ru ultra-fine particles, Ru alloy ultra-fine particles, Rh ultra-fine particles, Rh alloy ultra-fine particles, Ta ultra-fine particles, Ta alloy ultra-fine particles, Ir ultra-fine particles, Ir alloy ultra-fine particles, W ultra-fine particles and W alloy ultra-fine particles.
The hydrogen absorbing alloy powder has a very high activity attributable to its fine metallographic structure and hence, presents a large hydrogen storage capacity and a high rate of hydrogen absorption/desorption without conducting an activating procedure, because the powder is the aggregate of alloy particles each including the Mg matrix having the crystal grain size DC on the order of xcexcm, and the ultra-fine particles having the particle size d0 on the order of nm and dispersed in the Mg matrix, as described above.
However, if the crystal grain size DC is smaller than 1.0 xcexcm, the process of production of the hydrogen absorbing alloy powder is complicated and for this reason, it is difficult to mass-produce the hydrogen absorbing alloy powder. On the other hand, if DC greater than 500 xcexcm, the rate of hydrogen absorption/desorption presented by the hydrogen absorbing alloy powder is reduced. If the particle size d0 is smaller than 10 nm, the activity of the ultra-fine particles is too high and hence, it is difficult to handle the ultra-fine particles. On the other hand, if d0 greater than 500 nm, the hydrogen storage capacity in the hydrogen absorbing alloy powder is decreased, and the rate of hydrogen absorption/desorption is lowered.
In addition, according to the present invention, there is provided a hydrogen absorbing alloy powder which is an aggregate of alloy particles each including a Tixe2x80x94Fe alloy matrix and a plurality of ultra-fine particles dispersed in the Tixe2x80x94Fe alloy matrix, the Tixe2x80x94Fe alloy matrix including a plurality of Tixe2x80x94Fe alloy crystals having a grain size DC in a range of 1.0 xcexcmxe2x89xa6DCxe2x89xa6500 xcexcm, and the ultra-fine particles having a particle size d0 in a range of 10 nmxe2x89xa6d0xe2x89xa6500 nm, the ultra-fine particles being at least one type selected from the group consisting of Ni ultra-fine particles, Ni alloy ultra-fine particles, Fe ultra-fine particles, Fe alloy ultra-fine particles, V ultra-fine particles, V alloy ultra-fine particles, Mn ultra-fine particles, Mn alloy ultra-fine particles, Ti ultra-fine particles, Ti alloy ultra-fine particles, Cu ultra-fine particles, Cu alloy ultra-fine particles, Al ultra-fine particles, Al alloy ultra-fine particles, Pd ultra-fine particles, Pd alloy ultra-fine particles, Pt ultra-fine particles, Pt alloy ultra-fine particles, Zr ultra-fine particles, Zr alloy ultra-fine particles, Au ultra-fine particles, Au alloy ultra-fine particles, Ag ultra-fine particles, Ag alloy ultra-fine particles, Co ultra-fine particles, Co alloy ultra-fine particles, Mo ultra-fine particles, Mo alloy ultra-fine particles, Nb ultra-fine particles, Nb alloy ultra-fine particles, Cr ultra-fine particles, Cr alloy ultra-fine particles, Zn ultra-fine particles, Zn alloy ultra-fine particles, Ru ultra-fine particles, Ru alloy ultra-fine particles, Rh ultra-fine particles, Rh alloy ultra-fine particles, Ta ultra-fine particles, Ta alloy ultra-fine particles, Ir ultra-fine particles, Ir alloy ultra-fine particles, W ultra-fine particles and W alloy ultra-fine particles.
This hydrogen absorbing alloy powder also presents a large hydrogen storage capacity and a high rate of hydrogen absorption/desorption, as does the above-described hydrogen absorbing alloy powder. The grain size DC and the particle size d0 are limited for the same reason as described above.
Further, according to the present invention, there is provided a hydrogen-storing tank for mounting in a vehicle and including a hydrogen absorbing alloy powder therein, the hydrogen absorbing alloy powder being an aggregate of alloy particles each including an Mg matrix and a plurality of ultra-fine particles dispersed in the Mg matrix, the Mg matrix including a plurality of Mg alloy crystals having a grain size DC in a range of 1.0 xcexcmxe2x89xa6DCxe2x89xa6500 xcexcm, and the ultra-fine particles having a particle size d0 in a range of 10 nmxe2x89xa6d0xe2x89xa6500 nm, the ultra-fine particles being at least one type selected from the group consisting of Ni ultra-fine particles, Ni alloy ultra-fine particles, Fe ultra-fine particles, Fe alloy ultra-fine particles, V ultra-fine particles, V alloy ultra-fine particles, Mn ultra-fine particles, Mn alloy ultra-fine particles, Ti ultra-fine particles, Ti alloy ultra-fine particles, Cu ultra-fine particles, Cu alloy ultra-fine particles, Al ultra-fine particles, Al alloy ultra-fine particles, Pd ultra-fine particles, Pd alloy ultra-fine particles, Pt ultra-fine particles, Pt alloy ultra-fine particles, Zr ultra-fine particles, Zr alloy ultra-fine particles, Au ultra-fine particles, Au alloy ultra-fine particles, Ag ultra-fine particles, Ag alloy ultra-fine particles, Co ultra-fine particles, Co alloy ultra-fine particles, Mo ultra-fine particles, Mo alloy ultra-fine particles, Nb ultra-fine particles, Nb alloy ultra-fine particles, Cr ultra-fine particles, Cr alloy ultra-fine particles, Zn ultra-fine particles, Zn alloy ultra-fine particles, Ru ultra-fine particles, Ru alloy ultra-fine particles, Rh ultra-fine particles, Rh alloy ultra-fine particles, Ta ultra-fine particles, Ta alloy ultra-fine particles, Ir ultra-fine particles, Ir alloy ultra-fine particles, W ultra-fine particles and W alloy ultra-fine particles.
The hydrogen-storing tank includes therein the hydrogen absorbing alloy powder presenting a large hydrogen storage capacity and a high rate of hydrogen absorption/desorption, as described above and hence, is suitable to be mounted in a vehicle. The grain size DC and the particle size d0 are limited for the same reason as described above.